The present invention relates to the formation of coreless rolls of a stretchable plastic film, also referred to as stretch film, which is wound up on a special perforated mandrel conformed for enabling one or a plurality of coreless rolls to be simultaneously wound up and sequentially removed, wherein use is made of a pressurised air flow for causing some internal turns of the rolls to radially expand, so that said coreless rolls are made easy to be frictionless removed preventing the implosion of the rolls due to compaction and self-adhesion of a number of internal turns close to the mandrel. In particular, the invention is directed to a method as well as to a mandrel and an apparatus for winding up coreless rolls of a stretch film, the mandrel and the apparatus being suitable for actuating said method.
The invention has a particular application in the field of stretchable plastic films, normally used for packaging or for winding up palletized loads, or other similar applications, wherein the demands for improving the working cycle, reducing the costs for forming the rolls, as well as simplifying the problems for managing said rolls, result always more relevant.
Stretchable plastic films hold a preeminent position in packaging due to their excellent functional qualities; one of the characteristics that are distinguishing a stretchable plastic film from any other web material is its “cling”, that is the ability of the stretchable plastic film to adhere to itself creating a seal on the package.
Mechanical properties of a stretch film are also relevant in relation to the tear and pull resistance, with stretch values up to 100-140% and more, and a relatively low Young's modulus; use of stretch film in packaging have proved to reduce the amount of film consumption as much as 40-50%.
Furthermore use of correctly wound up coreless rolls of stretch-films having a number of compacted internal turns, which maintain a cylindrical shape of the rolls after the removal from the mandrel, that is suitably conformed to avoid any risk of implosion and deformation of their cylindrical shape, is a very relevant characteristic that makes the packaging and wrapping of palletized loads by stretch films, easier and faster, with significantly higher output. Therefore, the use of stretchable plastic films, in respect to other web materials and different technical fields, is very important.